Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quais estações de pesquisa árticas observaram mais de 50 espécies únicas?
 ###Tabelas: 
CREATE TABLE arctic_research_stations (id INT, name TEXT, location TEXT); INSERT INTO arctic_research_stations (id, name, location) VALUES (1, 'Toolik Field Station', 'Alaska'); INSERT INTO arctic_research_stations (id, name, location) VALUES (2, 'Zackenberg Research Station', 'Greenland'); INSERT INTO arctic_research_stations (id, name, location) VALUES (3, 'Koldeway Station', 'Norway'); CREATE TABLE species_observations (station_id INT, species_name TEXT); INSERT INTO species_observations (station_id, species_name) VALUES (1, 'Species A'); INSERT INTO species_observations (station_id, species_name) VALUES (1, 'Species B'); INSERT INTO species_observations (station_id, species_name) VALUES (2, 'Species A'); INSERT INTO species_observations (station_id, species_name) VALUES (2, 'Species C'); INSERT INTO species_observations (station_id, species_name) VALUES (3, 'Species A'); INSERT INTO species_observations (station_id, species_name) VALUES (3, 'Species B'); INSERT INTO species_observations (station_id, species_name) VALUES (3, 'Species C'); INSERT INTO species_observations (station_id, species_name) VALUES (3, 'Species D');
SELECT station_id, COUNT(DISTINCT species_name) as species_count FROM species_observations GROUP BY station_id HAVING species_count > 50;